Detector for fumes and combustion gases

ABSTRACT

An ionization detection means is disclosed having a housing, a reference ionization chamber and a sensing ionization chamber located in the housing. A radioactive source is also positioned in the housing and is arranged for causing ionization of particles within the chambers. A means is provided for establishing a flow path to the sensing chamber for atmospheric constituents such as fumes, vapors or aerosols. An electrical output signal is provided upon the occurrence of fumes, vapors or aerosols in the sensing chamber. A means is provided for storing information representative of the time elapsed between the initiation of the output signal and a subsequent point in time. A circuit means is also provided for indicating a defective condition in the operation of the detector. A predetermined atmosphere of pollutants is established within the reference chamber for precompensating for existing environmental pollutants.

United States Patent 1191 Gacogne 1 1 Sept. 30, 1975 DETECTOR FOR FUMESAND [73] Assignee: Societe Gamma Electronic, Paris.

France [22] Filed: Jan. 16, 1974 [21] Appl. No.: 433,621

[30] Foreign Application Priority Data June 4. 1973 France 73,201 l0[52] US. Cl 340/237 8; 250/381 [51] Int. Cl. G08B 21/00; 6088 17/10 [58]Field of Search 324/33; 340/237 S, 408;

[56] References Cited UNITED STATES PATENTS 3.500.368 3/1970 Nagao Abe340/237 8 3.530.450 9/1970 Waltharcl et al. 340/237 S 3.767.917 10/1973Lainpart et al. 340/237 S X Primary lituminer-Alfred E. Smith AssistantE.\'uminerRolf Hille Attorney Agent. or Firm-'Kaufman & Kramer [57]ABSTRACT An ionization detection means is disclosed having a housing, areference ionization chamber and a sensing ionization chamber located inthe housing. A radioactive source is also positioned in the housing andis arranged for causing ionization of particles within the chambers. Ameans is provided for establishing a flow path to the sensing chamberfor atmospheric constituents such as fumes, vapors or aerosols. Anelectrical output signal is provided upon the occurrence of fumes,vapors or aerosols in the sensing chamber. A means is provided forstoring information representative of the time elapsed between theinitiation of the output signal and a subsequent point in time. Acircuit means is also provided for indicating a defective condition inthe operation of the detector. A predeter mined atmosphere of pollutantsis established within the reference chamber for precompensating forexisting environmental pollutants.

13 Claims. 2 Drawing Figures I I +1 m 3 I ii 1 i ?!v I i L e0 I W 62[1?4 102 s al xts or P07625702- 63 l I l 06 94 I I I M US. Patent Sept.30,1975

Sheet 1 0f 2 US. Patent Sept. 30,1975 Sheet2of2 3,909,815

DETECTOR FOR FUMES AND COMBUSTION GASES The present invention relates toa detector for sensing the occurrence of fumes, gasesor aerosols whichmay, for example, beindicative of the existence of a fire. The inventionrelates more particularly to an improved form of ionization detector fordetecting fumes, gases or aerosols.

Ionization detectors adapted for sensing the occurrence of fumes, gasesor aerosols which may be indicative of the existence of a fire areknown. In one form of ionization detector, a reference ionizationchamber and a sensing ionization chamber are electrically coupled inseries. An electrode of the ionization chambers is common to each of thechambers and the potential of this common electrode will vary as gases,fumes or aerosols occur in the locale of the detector. The potential ofthe common electrode is applied to a circuit means which includes, forexample, a vacuum tube, a gaseous tube or a transistor. This circuitmeans is adapted for altering the state of an electrical signalingcircuit thereby providing an indication of the presence of the gaseousfumes or aerosols. lonizationdetectors of this type can be used in thevarious locations such as factories, shops, warehouses, archives,dwellings and the like for detection and monitoring of fumes andcombustion gases. v

Prior ionization detectors of the type referred to exhibit severallimitations. They are, for. example, undesirably susceptible to externalinfluences such as envivide an improved form of ionization detectionmeans which is adapted for sensing fumes, gases or aerosols.

Another object of the invention is to provide an ionization detectionmeans for sensing fumes, gases or aerosols and having means forproviding an indication of the origin and propagation of a tire orcombustion.

Another object of the invention is to provide an ionization detectionmeans for sensing fumes, gases or aerosols and which includes improvedmeans for compensating environmental pollutants in the atmosphere.

Another object of the invention is toprovide an ionization detectionmeans which provides the indication of a defective condition existing inthe detector.

A further object of the invention is to provide an ionization detectormeans which provides for reducing false indications caused by emissionsaccompanying the initiation of a tire.

Another object of the invention is to provide an improved ionizationdetection means which provides a quantitative and relative estimate ofthe magnitude of the fire or combustion. i v

In accordance with features of this invention, an ionization-detector isprovided having a housing, a reference ionization chamber and a sensingionization chamber located in said housing, a radioactive sourcearranged for causing ionization of particles within said chambers, meansfor providing access to said sensing chamber of atmospheric constituentssuch as fumes,

vapors or aerosols, means for providing an electrical output signal fromsaid chamber indicative of the presence of a fume, vapor or aerosol, andmeans for providing and storing information representative of the timeelapsed between the initiation of said output signal and a subsequentpoint in time. The stored information therefore provides data which, inconjunction with data from similar detection means, enables adetermination of the place of initiation and progress of a fire or othereliminates the need for electrically correcting for the alarm level ofthe detector. I

These and other objects and features of the invention will becomeapparent with reference to the following specification and to thedrawings wherein:

FIG 1 is an elevation view, partly in cross section, of anembodiment ofan ionization detector constructed in accordance with features of thisinvention; and

' FIG. 2 is a circuit diagram, partly in schematic form, of a circuitarrangement employed with the detector of FIG. 1. I

Referring now to FIG. 1 of the drawings, the detector is shown toinclude a housing comprising a rosette shaped base 1 and casing S. T hebase 1 is preferably formed of a high temperature, electrical insulatingmaterial. such as ceramic while the casing 5 is formed of ,an electricalconductingmaterial such as aluminum, steel, etc. A plurality of boresare formed in the base I and there is positioned in each of the bores afemale junctionconnector 2, An indicating means comprising 1 v and 32are provided and extend into the base through I an aperture 33 formedthereinand are coupled through screw terminals to the female connectors2.

v The casing 5 comprises the'principal body of the detector and isthreaded at one end 34 for engaging a threaded shoulder segment of thebase 1. A disc shaped plate 6'is mounted to the'walls of the casing 5and supports male connectors 4 which extend from this plate and whichengage the female connectors 2 in the base 1. In addition, electroniccircuitry in the form of componentsand a printed circuit as described ingreater detail hereinafter is mounted to the plate 6 as is an inner or'reference ionization chamber 7. l

The inner or reference ionization chamber 7 includes a positiveelectrode 13 which is connected to a printed circuit mounted on theplate 6 by a centrally located rod 114. A cathode electrode 15 of thereference chamber is positioned about the anode electrode 13.

' This cathode electrode along with a disc 16 formed of an electricallyinsulating material is positioned in the casing 5 in a manner forproviding an enclosed chamber within the confined volume defined by theelectrode l5 and the disc 16. This arrangement inhibits access of moistair to the electronic parts.

A radioactive source 17 is mounted within the reference chamber 7 andthe radiation from this source causes, ionization of particles withinthe chamber and a resultant current flow between the electrodes 13 and15. The radioactive source 17 is preferably an alpha emitter which doesnot emit radioactive gases such as plutonium-239 or americium-24l orequivalent. The electrodes 13 and 15 may be spaced relatively close toone another thereby enhancing the creation of an ionization current ofsignificant magnitude yet requiring only a relatively small operatingpotential between the electrodes.

An outer or analysis" ionization chamber 23 is provided and is definedby the electrode 15 of the inner chamber, a wall segment of the casing5, a plurality of fins extending about the circumference and surface ofthe casing 5 and which provide access for fumes, aerosols and vapors tothe analysis chamber through a grating 19. The grating 19 is secured inposition against the fins by belts or rings 20 and 21. The electrodes ofthe analysis chamber include the electrode 15 which is common to boththe reference and analysis chamber and which functions as a relativelypositive electrode in the analysis chamber. The negative electrodecomprises a disc 12 which is mounted from a surface 10 by an adjustmentscrew 36 and which provides for varying the spacing between the disc 12and the electrode 15. Adjustment of the position of electrode 12compensates for manufacturing tolerances and, in addition, provides foroptimum spacing between electrodes 12 and 15; particularly when theanalysis chamber is subjected to strong air currents. A radioactiveionization source 18 similar to a source 17 is also mounted in thechamber and is positioned for causing ionization of the particles andestablishment of a current between the electrodes 12 and 15. The casingbody 5, the fins and the grating are conductively intercoupled and areconnected to a negative terminal of a source of operating potential.This results in a Faraday-cage form of protection which shields orremoves the electric components and particularly field effecttransistors within a device from the influence of external electricfields.

It is noted that the fin and grid structure operate to reduce theadverse effect of substantial air currents and resulting false alarms.Gases or fumes which enter the analysis chamber flow between the finswhich are relatively thin and which are spaced relatively closetogether. These fins are shaped and sizedfor providing that the flowpassage presented to air currents is reduced with respect to the crosssection of the analysis chamber. In addition to maintaining the grid inposition, the belts 20 and 21 also reduce the effective surface area ofthe grid which is presented to the surrounding environment. Thus, aircurrents, which tend to disturb the distribution of ions in the analysischamber and to alter the potential of the common electrode issubstantially neutralized.

A relatively low potential difference is applied between the elcctrodesl3 and 12 of the reference and measuring chambers respectively. Thispotential is on the order of 50 volts or less. The potential at theelectrode 15. which is common to both chambers, is coupled to anelectronic circuit which is provided for modifying the state of anelectric or an electronic signaling circuit in accordance with changesoccurring in ionization within the outer or analysis chamber.

In accordance with a feature of this invention, an atmosphere isestablished within the reference chamber for compensating forenvironmental pollutants. This is accomplished in one manner by placinga container containing a solid mixture of sodium carbonate, nickelcarbonyl and an alkali sulfide in an enclosure. A partial vacuum is thenproduced and atmospheric pressure is then re-established. The CO level,which should correspond to 3 mg/m of CO, is then measured. The finishedunsealed ampoules are then stored in this enclosure for several daysprior to the final assembly. This process can be shortened at times bycontamination of the ampoule in situ.

Referring now to the circuit arrangement of FIG. 2, operating potentialfor the detector is derived from an external source 40 which maycomprise a battery pack and is applied via input leads 30 and 31 to thefemale connectors 2 which are located in the base 1. A relativelypositive potential is also coupled to the indicator lamp 3. The outputpotential of the source 40 which may for example comprise 25 volts isapplied to the various components of the circuit arrangement through astabilizing network comprising a resistor 42 and a zener diode 94. Thisstabilized positive potential is applied to the electrode 13 of thereference chamber and a negative potential to the electrode 12 of theanalysis chamber. When a substantially constant potential difference isestablished between the positive electrode 13 of the reference chamberand the negative electrode 12 of the analysis chamber, both of whichchambers are rendered conductive by the radioactive ionization means,then a small ionization current circulates and the potential of thecommon electrode 15 will attain an equilibrium magnitude which dependson various factors including the level of ionization created by theradiation sources, the shape of the electrodes, and the relativedimensions of the two chambers. This potential is applied to a gateelectrode 44 of a junction field effect transistor 46. The positiveoperating potential is also applied to an electrode 48 of thistransistor while the negative potential is applied to an electrode 50 ofthe transistor 46 through a series resistive network which includesresistors 52 and 54 and a potentiometer A control circuit is providedfor causing energization of the lamp 3 when vapors, fumes or aerosolsare detected or when a defective condition in the ionization chambersresults in a detector fault. A lead 58 of the lamp 3 is coupled to thepositive input line 30 while a lead 60 of the lamp 3 is coupled througha terminal 62 and the female and male connectors of the detector to ananode electrode 64 of a thyristor 66. A negative electrode 68 of thethyristor is connected to the negative input potential. When a triggersignal is applied to a gate electrode 70 of the thyristor 66, thethyristor is switched into a conductive state and the lamp 3 is therebyenergized providing an indication of the presence of fumes, gases oraerosols of the existence of a faulty condition in the detector.

Trigger signals which are applied to the gate electrode 70 are appliedthrough alternative circuit means, depending on whether a defect orfault in the installation or operation of the chambers occurs or whetherduring proper operation of the chambers a vapor, gas

or aerosol is detected ln the former case, the defect is indicated by apotential at the junction of the resistors 52 and 54. This potential isapplied through a resistance 72 to the base electrode 74 of an NPNtransistor 76. Operating potential is applied to the transistor 76through a resistor 78 which is coupled between the resistor 42 and acollector electrode 80 of the transistor 76 while a negative potentialis applied to an emitter electrode 82 of this transistor. A diode 84 isprovided for coupling a triggering signal from the transistor 76 to thegate electrode 70 of the thyristor. The diode 84, under ordinaryoperating conditions and in the absence of defective operation of thechamber is back-biased as a result of the potential established at thisdiode by a resistor 86 and by the potential of the collector electrode80 of the transistor 76. The potential at the collector electrode 80 isestablished at a relatively low positive value by selecting a baseresistive impedance 72 which provides for conduction of the transistorwhen a potential, which is indicative of proper operation of thechambers, exists at the junction of the resistors 52 and 54.

Alternatively, the thyristor 66 is triggered into conduction whenvapors, gases or aerosols are detected by a signal which is derived froma wiper arm 88 of the potentiometer 56 and is applied to the gateelectrode 70 through a zener diode 90.

In operation, the reference and analysis chambers under no fault, novapor, gas or aerosol conditions provide a potential at the commonelectrode which results in a potential at the junction of the resistors52 and 54 having a magnitude for causing conduction of the transistor76. The diode 84 is therefore backbiased. Similarly, the potential atthe wiper arm 88 under these conditions has a magnitude insufficientlyhigh for causing conduction of the zener diode 90. In this regard, thesensitivity of the detector to vapors, gases and aerosols is adjustableby adjustment of the wiper arm 88 of the potentiometer 56. In FIG. 1, anaperture 92 is formed in the casing 5 for providing access to thepotentiometer for a sensitivity adjustment of the wiper arm 88. Adefective installation or operation or abuse of the detector can resultin a defect in insulation. In the analysis chamber this defect ininsulation will be reflected as an abnormal drop in the equilibriumpotential of the electrode 15 resulting in a decrease in the basecurrent to the transistor 76. The collector voltage of this transistorthen rises causing forward bias and conduction of the diode 84. Theforward biased diode 84 provides a current passage through theresistance 78 to the gate electrode 70 of the thyristor 66, therebyswitching the thyristor into a conductive condition and causingenergization of the lamp 3. The lamp will then remain energized untiloperating potential is interrupted to the thyristor 66.

In the alternative and principal mode of operation, the entry of avapor, gas or aerosol into the analysis chamber results in anappreciable decrease in the magnitude of the ionization current, therebyincreasing the impedance of this chamber and causing an increase in thepotential of the electrode 15 from its equilibrium value. The voltage atthe potentiometer wiper arm 88 will accordingly increase from thecorresponding equi-- librium potential to a magnitude at which the zenerdiode 90 becomes conductive and thereby triggers the thyristor 66 intoconduction. The lamp 3 is then energized and remains energized untiloperating potential to the thyristor 66 is interrupted.

It is beneficial at times to provide an indication of the initiation orof the progress of a fire or other disaster.

In accordance with another feature of this invention, the detectorincludes a memory for establishing such an indication. The distributionof a number of such detectors about the site of a fire or disaster, thenrenders it possible to determine the initiation and duration of the fireat each detector station and to consequently trace the progress of thefire or disaster. An integrating circuit means is provided by the use ofa field effect transistor 94 which is coupled to an operationalamplifier 96 having a feedback loop and arranged as an integrator. InFIG. 2, the anode electrode 64 of the thyristor 66 is coupled to a gateelectrode 93 of a field effect transistor 94. The field effecttransistor 94 is coupled in series with an integrator 96. The integrator96 comprises a solid state integrated circuit. One such integratedcircuit suitable for'the use indicated is SN521 manufactured by TexasInstruments, Inc. This integrator is thermally insulated with asbestosfor example in order to protect the integrator from the effects of thefire or disaster. An output from the integrator 96 is applied via theline 29 to a remote electronic storage means 98. The storage means 98comprises for example a totalizer counter or a binary counter. Duringthe interval of time in which vapors, fumes or aerosols are detected ora fault condition exists, the integrator 96 provides a periodicallyrecurring output voltage. Either the analog representation of theintegrator output or the digital representation which are indicative ofthe total time during which the faulty condition existed can be usedsubsequently to determine the intensity and duration of the faultycondition. This information in turn is employed to obtain geographicalindications of the origin of the faulty condition. This is accomplishedfor I example by obtaining the different records from a number ofdetectors located at the fire or disaster site and correlating theserecords to establish a map of the location and distribution of thedisaster.

A circuit arrangement comprising resistors 100 and 102 and a diode 104are provided for generating a signal for coupling to a central location.This signaling is particularly useful when defects such as aninterruption in the application of power to the unit from the source 40occurs. This may occunfor example when the casing 5 is separated fromthe base 1. The conduction of the thyristor 66 upon the occurrence of adefect results in a relatively low potential at the terminal 62. Theresistor 102 is selected to have a relatively low resistance withrespect to the resistor 100. When a relatively low potential occurs atterminal 62 and since a positive potential is applied to the resistor100, the diode 104 will be conducting and a relatively low potentialwill appear on the output line 106. It is noted that other detectorssensing for similar or other conditions may be coupled to the line 106.When the supply to the unit is interrupted such as through the removalof a detector from its base, the potential at the point 106 will riseand this rise can be utilized for indicating or control purposes at amain panel.

An improved form of ionization detection means for gases, vapors oraerosols has thus been described. The detection means advantageouslycompensates for a level of pollution in an environment where thedetector is to be utilized. In addition, the detection means providesmeans for recording the duration of a false alarm or of the detection ofvapors, gases or aerosols and provides an indication which can be storedin a counter. The detection means further is adapted for indicating afaultcondition in the detector. 7

While particular embodiments of the invention have been describedherein, it will be apparent to those skilled in the art that variationsmay be made thereto without departing from the spirit of the inventionand the scope of the appended claims.

What is claimed is: 1. An ionization detector for detecting fumes,vapors or aerosols comprising:

a reference ionization chamber and a sensing ionization chamberpositioned within a housing; a radioactive means arranged for causingthe ionization of particles within said chambers; means for providing aflow path for atmospheric 7 fumes, vapors or aerosols from anenvironment within which the detector is located to said sensingchamber; means for providing an electrical output signal from saidchambers indicative of the presence of a fume, vapor or aerosol in saidsensing chamber; and circuit storage means coupled to said latter meansand means responsive to said electrical signal for providing anindication of the elapsed time between the initial occurrences of thefumes, vapors or aerosols in the sensing chamber and a subse-' quentinstant of time.

2 An ionization detector for detecting fumes, vapors or aerosolscomprising:

a reference ionization chamber and a sensing ionization chamberpositioned within a housing:

a radioactive means arranged for causing the ionization of particleswithin said chambers;

means for providing a flow path for atmospheric fumes, vapors oraerosols from an environment within which the detector is located tosaid sensing chamber; means for providing an electrical output signalfrom said chambers indicative of the presence ofa fume, vapor or aerosolin said sensing chamber; and

electrical circuit storage means and circuit means responsive to saidoutput signal for causing said electrical circuit storage means tocontinuously accumulate a sum after an initial occurrence of said outputsignal and providing an indication of the elapsed time between theinitial occurrences of the fumes, vapors or aerosols in the sensingchamber and a subsequent instant of time.

3. The detection means of claim 2 wherein said electrical storage meanscomprises a counter.

4. The detection means of claim 3 wherein said circuit means for causingsaid storage means to accumulate a sum comprises a circuit arrangementfor generating periodically recurring impulses.

5. The detection means of claim 4 wherein said circuit means forgenerating periodically recurring pulses comprises an operationalamplifier having a feedback network coupled thereto for causing saidamplifier to function as an integrating means.

6. An ionization detector for providing an indication of the presence offumes, vapors or aerosols comprising:

a reference ionization chamber and a sensing ionization chamberpositioned in a housing;

each of said ionization chambers having an anode electrode and a cathodeelectrode; said ionization chambers coupled electrically in series andhaving a cathode electrode of one of said chambers and an anodeelectrode of the other of said chambers which is common to each of saidchambers; a switching circuit means; electrical storage means coupled tosaid switching circuit means and de-energized by said switching meanswhen said switching circuit means exists in a first of two states andenergized when said switching circuit means exists in a second of twostates;

circuit means coupled between said switching circuit means and saidstorage means for providing a continuous entry to said storage meanswhen said switching means exists in said second state; and

circuit means coupled between said common electrode and said switchingcircuit means for causing said switching circuit means to exist in saidfirst state during the absence of vapors, fumes or aerosols within saidsensing chamber and for causing said switching circuit means to switchto said second state when vapors, fumes or aerosols exist in saidsensing chamber.

7. The detection means of claim 6 wherein said indicating meanscomprises an electrically energized indicator which provides anindication which is perceptible by the human senses.

8. The detection means of claim 7 wherein said indicating meanscomprises a visual indicator mounted on said housing.

9. The detection means of claim 6 wherein said indicating meanscomprises an electrical storage means and circuit means for providing acontinuous entry to said storage means when said switching means existsin said second state.

10. An ionization detector for sensing vapors, fumes and aerosolscomprising:

a reference ionization chamber and a sensing ionization chamberpositioned within the housing;

each of said ionization chambers having a cathode and an anodeelectrode;

radioactive means arranged for causing ionization of particles withinsaid chambers;

means for providing access to said sensing chamber for environmentalconstituents such as fumes, vapors or aerosols which are to be detected.

said reference chamber adapted to inhibit the entry of environmentalconstituents into the reference chamber and to maintain a predeterminedenvironment established therein; said reference chamber containing apredetermined level of environmental pollutants corresponding to thelevel of pollutants existing in the environment within which as detectoris to be located; and

means coupled to said chambers for providing an indication of theexistence of fumes, vapors or aerosols in said sensing chamber.

11. The detection means of claim 10 wherein said reference chambercontains carbon monoxide at a concentration of 3 mg/m.

12. An ionization detector for providing an indication of the presenceof fumes, vapors or aerosols comprising:

a reference ionization chamber and a sensing ionization chamberpositioned in a housing;

each of said ionization chambers having an anode electrode and a cathodeelectrode;

said ionization chambers coupled electrically in series and having acathode electrode of one of said chambers and an anode electrode of theother of said chambers which is common to each of said chambers; aswitching circuit means; electrical storage means coupled'to saidswitching circuit means and de-energized by said switching means whensaid switching circuit means exists in a first of two states andenergized when said switching circuit means exists in a second of twostates;

circuit means coupled between said common electrode and said switchingcircuit means for causing said switching circuit means to exist in saidfirst state during the absence of vapors, fumes or aerosols within saidsensing chamber and for causing said switching circuit means to switchto said second state when vapors, fumes or aerosols exist in saidsensing chamber; and,

circuit means for causing said switching means to alternatively switchto said second state upon the occurrence of a fault in the operation ofsaid ionization chambers.

13. An ionization detector for providing an indication of the presenceof fumes, vapors or aerosols comprising:

a reference ionization chamber and a sensing ionization chamberpositioned in a housing;

each of said ionization chambers having an anode electrode and a cathodeelectrode;

said ionization chamber coupled electrically in series and having acathode electrode of one of said chambers and an anode electrode of theother of said chambers which is common to each of said chambers;

a first switching circuit means including a thyristor having an inputtrigger electrode;

indicating means coupled to said switching circuit means andde-energized by said switching circuit means when said switching circuitmeans exists in a first of two states and energized when said switchingcircuit means exists in a second of two states;

circuit means coupled between said common electrode and said switchingcircuit means for causing said switching circuit means to exist in saidfirst state during the absence of vapors, fumes or aerosols within saidsensing chamber and for causing said switching circuit means to switchto said second state when vapors, fumes or aersols exist in said sensingchamber, said circuit means comprising a field effect transistoramplifier circuit arrangement having an impedance coupled in anelectrode circuit of the field effect transistor, and a voltagesensitive switching means coupled between said impedance and said inputtrigger electrode of said thyristor; and,

amplifier circuit means having an input thereto coupled from theimpedance of said field effect transistor circuit arrangement andswitching means coupled between said amplifier and said input triggerelectrode of said thyristor, said switching means operative to couplesaid amplifier to said thyristor input trigger electrode upon theoccurrence of a fault in said sensing ionization chamber.

1. An ionization detector for detecting fumes, vapors or aerosolscomprising: a reference ionization chamber and a sensing ionizationchamber positioned within a housing; a radioactive means arranged forcausing the ionization of particles within said chambers; means forproviding a flow path for atmospheric fumes, vapors or aerosols from anenvironment within which the detector is located to said sensingchamber; means for providing an electrical output signal from saidchambers indicative of the presence of a fume, vapor or aerosol in saidsensing chamber; and circuit storage means coupled to said latter meansand responsive to said electrical signal for providing an indication ofthe elapsed time between the initial occurrences of the fumes, vapors oraerosols in the sensing chamber and a subsequent instant of time.
 2. Anionization detector for detecting fumes, vapors or aerosols comprising:a reference ionization chamber and a sensing ionization chamberpositioned within a housing: a radioactive means arranged for causingthe ionization of particles within said chambers; means for providing aflow path for atmospheric fumes, vapors or aerosols from an environmentwithin which the detector is located to said sensing chamber; means forproviding an electrical output signal from said chambers indicative ofthe presence of a fume, vapor or aerosol in said sensing chamber; andelectrical circuit storage means and circuit means responsive to saidoutput signal for causing said electrical circuit storage means tocontinuously accumulate a sum after an initial occurrence of said outputsignal and providing an indication of the elapsed time between theinitial occurrences of the fumes, vapors or aerosols in the sensingchamber and a subsequent instant of time.
 3. The detection means ofclaim 2 wherein said electrical storage means comprises a counter. 4.The detection means of claim 3 wherein said circuit means for causingsaid storage means to accumulate a sum comprises a circuit arrangementfor generating periodically recurring impulses.
 5. The detection meansof claim 4 wherein said circuit means for generating periodicallyrecurring pulses comprises an operational amplifier having a feedbacknetwork coupled thereto for causing said amplifier to function as anintegrating means.
 6. An ionization detector for providing an indicationof the presence of fumes, vapors or aerosols comprising: a referenceionization chamber and a sensing ionization chamber positioned in ahousing; each of said ionization chambers having an anode electrode anda cathode electrode; said ionization chambers coupled electrically inseries and having a cathode electrode of one of said chambers and ananode electrode of the other of said chambers which is common to each ofsaid chambers; a switching circuit means; electrical storage meanscoupled to said switching circuit means and de-energized by saidswitching means when said switching circuit means exists in a first oftwo states and energized when said switching circuit means exists in asecond of two states; circuit means coupled between said switchingcircuit means and said storage means for providing a continuous entry tosaid storage means when said switching means exists in said secondstate; and circuit means coupled between said common electrode and saidswitching circuit means for causing said switching circuit means toexist in said first state during the absence of vapors, fumes oraerosols within said sensing chamber and for causing said switchingcircuit means to switch to said second state when vapors, fumes oraerosols exist in said sensing chamber.
 7. The detection means of claim6 wherein said indicating means comprises an electrically energizedindicator which provides an indication which is perceptible by the humansenses.
 8. The detection means of claim 7 wherein said indicating meanscomprises a visual indicator mounted on said housing.
 9. The detectionmeans of claim 6 wherein said indicating means comprises an electricalstorage means and circuit means for providing a continuous entry to saidstorage means when said switching means exists in said second state. 10.An ionization detector for sensing vapors, fumes and aerosolscomprising: a reference ionization chamber and a sensing ionizationchamber positioned within the housing; each of said ionization chambershaving a cathode and an anode electrode; radioactive means arranged forcausing ionization of particles within said chambers; means forproviding access to said sensing chamber for environmental constituentssuch as fumes, vapors or aerosols which are to be detected. saidreference chamber adapted to inhibit the entry of environmentalconstituents into the reference chamber and to maintain a predeterminedenviRonment established therein; said reference chamber containing apredetermined level of environmental pollutants corresponding to thelevel of pollutants existing in the environment within which as detectoris to be located; and means coupled to said chambers for providing anindication of the existence of fumes, vapors or aerosols in said sensingchamber.
 11. The detection means of claim 10 wherein said referencechamber contains carbon monoxide at a concentration of 3 mg/m3.
 12. Anionization detector for providing an indication of the presence offumes, vapors or aerosols comprising: a reference ionization chamber anda sensing ionization chamber positioned in a housing; each of saidionization chambers having an anode electrode and a cathode electrode;said ionization chambers coupled electrically in series and having acathode electrode of one of said chambers and an anode electrode of theother of said chambers which is common to each of said chambers; aswitching circuit means; electrical storage means coupled to saidswitching circuit means and de-energized by said switching means whensaid switching circuit means exists in a first of two states andenergized when said switching circuit means exists in a second of twostates; circuit means coupled between said common electrode and saidswitching circuit means for causing said switching circuit means toexist in said first state during the absence of vapors, fumes oraerosols within said sensing chamber and for causing said switchingcircuit means to switch to said second state when vapors, fumes oraerosols exist in said sensing chamber; and, circuit means for causingsaid switching means to alternatively switch to said second state uponthe occurrence of a fault in the operation of said ionization chambers.13. An ionization detector for providing an indication of the presenceof fumes, vapors or aerosols comprising: a reference ionization chamberand a sensing ionization chamber positioned in a housing; each of saidionization chambers having an anode electrode and a cathode electrode;said ionization chamber coupled electrically in series and having acathode electrode of one of said chambers and an anode electrode of theother of said chambers which is common to each of said chambers; a firstswitching circuit means including a thyristor having an input triggerelectrode; indicating means coupled to said switching circuit means andde-energized by said switching circuit means when said switching circuitmeans exists in a first of two states and energized when said switchingcircuit means exists in a second of two states; circuit means coupledbetween said common electrode and said switching circuit means forcausing said switching circuit means to exist in said first state duringthe absence of vapors, fumes or aerosols within said sensing chamber andfor causing said switching circuit means to switch to said second statewhen vapors, fumes or aersols exist in said sensing chamber, saidcircuit means comprising a field effect transistor amplifier circuitarrangement having an impedance coupled in an electrode circuit of thefield effect transistor, and a voltage sensitive switching means coupledbetween said impedance and said input trigger electrode of saidthyristor; and, amplifier circuit means having an input thereto coupledfrom the impedance of said field effect transistor circuit arrangementand switching means coupled between said amplifier and said inputtrigger electrode of said thyristor, said switching means operative tocouple said amplifier to said thyristor input trigger electrode upon theoccurrence of a fault in said sensing ionization chamber.